Air speed indicator



Jan. 28, 1941. w. HELMORE AIR SPEED INDICATOR Filed May 6, 1940 Patented Jan. 28, 1941 2,229,749

UNITED STATES PATENT OFFICE AIR. SPEED INDICATOR William Helmore, Cambridge, England Application May 6, 1940, Serial No. 333,695 In Great Britain March 11, 1939 8 Claims. (Cl. 73182) This application corresponds to the applicathe balance of pneumatic pressures on the movtion of William Helmore, Serial No. 7891/39, able member is changed. A bleed passage for which was filed in Great Britain on March 11, the ice-controlled pneumatic pressure acting 1939. upon the movable member is conveniently con- I This invention relates to air speed indicators nected to a static head of the indicator.

for aircraft and is concerned with such indi- According to a further feature of the invencators of the kind in which the change of pneution electrical heating means of the Pitot head matic pressure at a Pitot head disposed in the is controlled by the movable member to put the 'air stream is conveyed to and indicated by a heating means into operation when ice forms at 10 pressure-sensitive instrument remote from the the detector. In one form of the indicator in 10 Pitot head, the Pitot head being provided with which an ice-accretion detector is employed havheating means for the prevention of ice deposits ing electric heating means for heating that part thereon. a of the detector disposed in the air stream, the

In air speed indicators of the kind referred movable member of the detector serves to conto heat is usually supplied to the Pitot head by trol both the heating means of the Pitot head ll passing an electric current through a heater eleand the heating means of the detector. In anment situated at or in the Pitot head. Norother form a single heating means is employed mally, the heating means is controlled either for heating both the Pitot head and the part of manualy by the pilot or by the operation of the ice-accretion detector disposed in the air so other electrical apparatus with the result that stream. a considerable wastage of electrical energy takes The invention also includes an air speed indiplace from the unnecessary operation of the cator as aforesaid in which the Pitot head and heater either through the neglect of the pilot the ice-accretion detector are constructed as a or by reason of the operation of the other elecunit device.

trical apparatus when ice is not present. A fur- Specific embodiments of the invention are 25 ther disadvantage occurs, when a manual conshown diagrammatically and by way of example trol of the Pitot head heater is employed, owing in the accompanying drawing, in which: to the fact that failure by the pilot to put the Figure 1 shows an air speed indicator with heater into operation when ice is present may heating means controlled by a separate ice-acresult in incorrect readings of air speed and v cretion detector, and

consequent danger to the aircraft. Figure 2 shows a construction of Pitot head and The present invention comprises an air speed ice-accretion detector for controlling heating of indicator of the kind referred to wherein the the Pitot head as aunit device;

heating means of the Pitot head is controlled Fi r 3 hows a modific n of he a r e- 86 by an ice-accretion detector so as to provide merit S ow n Figure heating of the Pitot head only when ice is pres- Like references indicate like parts in the sevent. The term ice accretion detector? is emeral figures of the drawing.

ployed herein to designate a device operable in Referring to Figure 1 of the drawing, the air response to the formation of ice, as distinguished speed indicator comprises a pneumatic pressure from devices which are responsive merely to head III having a Pitot head ll mounted in an 40 temperature change. outer casing I 2 constituting a static head and In one arrangement the ice-accretion detector for this purpose having lateral openings l3. For

employed comprises a part disposed in the air preventing ice formation on the Pitot head it is stream and having one or more apertures of provided with an electrical heating coil H.

such size as to be blocked by ice particles to The pneumatic pressure head is associated with 45 produce a change of pneumatic pressure acting a pressure-sensitive indicating instrument l5 upon a movable member, and according to a having a sealed casing I6 containing a closed further feature of the invention the Pitot head ll psi l p le I fixed at one side I8 to of the air speed indicator is connected to apply the casing I6 and having the other, movable an opposing pneumatic pressure on this movable side I9 connected to an indicating pointer 20. 50 member. The one or more apertures 01' the ice- The Pitot head is connected by a pipe 2| to the accretion detector become blocked by ice parcapsule l1 and the static head [2 is connected ticles before the formation of ice can materially by a pipe 22 to the casing of the instrument. affect the Pitot head which is considerably larger The ice-accretion detector comprises a tubular N in size, so that when ice forms on the detector part 23 which is placed in the air stream. This part 23 has a small aperture at the front, this aperture being considerably smaller in. diameter than the diameter of the Pitot head M. It is thus very liable to become blocked by ice parf ticles under ice forming conditions.

A two-part casing 25 is divided by a flexible diaphragm 26. The upper part of this casing is connected by a pipe 2'17 to the tubular part 23 of the ice-accretion detector and the lower part of the casing is connected by a pipe 28 to the Pitot head.

The diaphragm 25 carries a stud 33 arranged. to engage the free end of a spring contact Si secured at its other end to a terminal 32 on the casing 25. The free end of the spring contact 3t is arranged to co-operate with a terminal 33 on the casing, both the terminals 32 and 33 being insulated from the casing.

The terminal 32 is connected to one pole of a battery 34 and to one end of the heating coil 14 of the Pitot head. The other pole of the battery 34 is connected to one terminal of an electro-magnet 35, the other terminal of which is connected to the terminal 33. This electromagnet controls an armature 36 which on the electro-magnet being energised moves to close contacts 3! to complete a circuit from the battery 34 directly through the heating coil i i.

In operation, and in the absence of ice the pressures at the two sides of the diaphragm 26 will be substantially equal and the free end of the spring contact 3! will be separated from the terminal 33. Immediately ice begins to form it will close the aperture 25 and the pressure in the upper part of the casing 25 will leak away through a pipe 38 connected to the static head 12. The Htot head will not ice up so readily, due to its larger size, and the pressure applied from the Pitot head to the lower part of the casing 25 will deflect the diaphragm so as to cause the spring contact 3i to engage the terminal 33. A circuit will therefore be completed through the battery 34 and the electro-magnet 35. The electro-magnet being thus energised closes the contacts 31 to complete a circuit through the battery 34 and the heating coil H of the Pitot head. The heating of the Pitot head will prevent the formation of ice on it and the heating continues until the atmospheric conditions have caused the disappearance of the ice from the aperture 24 of the detector. It will be appreciated that a plurality of Pitot heads may be similarly linked to an ice-accretion detector for controlling the heating means of the Pitot head.

In a modification shown in Figure 3 the part 23 of the ice-accretion detector is provided with a heating coil 39 connected in parallel with the heating coil ll of the Pitot head ll. When ice forms to close the aperture 24 a circuit will be completed through the coil 39 in addition to the circuit which is completed through the coil H. The heat produced by the coil 39 will, after a short time, thaw the ice obstructing the aperture 24 so that in consequence the diaphragm 26 will be operated to interrupt the circuit through the electro-magnet 35 and in turn open the circuits of the heating coils 39 and M. Therefore, under ice forming conditions the heating means for the part 23 of the ice-accretion detector and the heating means for the Pitot head will be intermittently operated, and having regard to this intermittent operation the heating coil ll will be such as to provide adequate heat to prevent ice formation at the Pitot head.

In the construction shown in Figure 2 the speci ic pressure head and the ice-accretion detector are constructed as a single unit. In this construction the Pitot head Hi, the part 23 of the iceaccretion detector, with its aperture 24, and the diaphragm 26 with its two-part casing 25 are mounted in a single housing at constituting a static head, and for this purpose having the lat-- eral openings at it. A single electric heating coil 36 is provided around the Pitot head it and the part 23 of the ice-accretion detector, the coil being connected in an electric circuit of the same form as that shown in Figure 1. Thus, one end. of the coil is connected to the terminal 32 on which the contact spring M is mounted, and also to the battery 36, the other end of the coil being connected to the armature 38. The terminal 33 with which the contact spring 3i co-operates is connected to the electro-rnagnet 35. It will be seen that in this construction the aperture 24 of the ice-accretion detector communicates by a passage i277 with the casing 25 at that side of the diaphragm 28 having the spring contact 3| and the Pitot head i l communicates by a branch passage 528 with the casing 25 at the other side of the diaphragm 28. A bleed passage B38 is provided between the passage l2! and the static head. The Pitot head i l and the static head are connected respectively by pipes 20 and 22 to the indicating instrument, as shown in Figure 1.

By means of this invention a considerable economy in electrical energy is secured and the pilot is relieved of any responsibility for the operation of the heating means for the Pitot head. Moreover, the possibility of inaccurate estimation of air speed under ice forming conditions through neglect to put the heating means for the Pitot head into operation, is automatically avoided. Furthermore, with the use of an ice-accretion detector requiring a Pitot pressure a simplification is obtained by deriving this pressure from the Pitot head of the air speed indicator itself.

I claim:

1. An air speed indicator comprising a Pitot head, pressure-sensitive indicating means operated by changes of pneumatic pressure at the Pitot head, heating means for the Pitot head, an ice-accretion detector and means operated by the said detector for controlling said heating means to provide heating of the Pitot head only when ice is present.

2. An air speed indicator comprising a Pitot head, pressure-sensitive indicating means operated by changes of pneumaticpressure at the Pitot head, heating means for the Pitot head, an ice-accretion detector, said detector comprising a part in which a pneumatic pressure is produced and having an aperture which becomes blocked by the ice particles to produce a change of the pneumatic pressure in said part, a pressure movable member and means for applying the pneumatic pressure in said part to the movable member, means for applying the pneumatic pressure at the Pitot head as an opposing pressure on said movable member and means operated by said movable member. to control said heating means so as to provide heating of the Pitot head only when ice is present.

3. An air speed indicator comprising a Pitot head, pressure-sensitive indicating means operated by changes of pneumatic pressure at the Pitot head, electrical heating means for the Pitot head, an ice-accretion detector, said detector comprising a part in which a pneumatic pressure is produced and having an aperture which becomes blocked by the ice particles to produce a change of the pneumatic pressure in said part, a pressure movable member and means for applying the pneumatic pressure in said part to the movable member, means for applying the pneumatic pressure at the Pitot head as an opposing pressure on said movable member and switch means operated by said movable member to control said electrical heating means so as to provide heating of the Pitot head only when ice is present.

4. An air speed indicator comprising a Pitot head, pressure-sensitive indicating means operated by, changes of pneumatic pressure at the Pitot head, heating means for the Pitot head, an ice-accretion detector, said detector comprisinga part in which a pneumatic pressure is produced and having an aperture which becomes blocked by the ice particles to produce a change of pneumatic pressure in said part, a pressure movable member, means applying the pneumatic pressure in said part to the movable member and heating means for said part or the ice-accretion detector, means for applying the pneumatic pressure at the Pitot head as an opposing pressure on said movable member, and means operated by said movable member to control both the heating means 01 the Pitot head and the heating means of said part of the ice-accretion detector.

5. An air speed indicator comprising a Pitot head, pressure-sensitive indicating means operated by changes of pneumatic pressure at the Pitot head, an ice-accretion detector, said detector comprising a part in which a pneumatic pressure is produced and having an aperture which becomes blocked by the ice particles to produce a change of the pneumatic pressure in said part, a pressure movable member and means applying the pneumatic pressure :to the movable member, means for applying the pneumatic pressure at the Pitot head as an opposing pressure on said movable member, a single electric heating means for heating both the Pitot head and the said part of the ice-accretion detector and means operated by said movable member for controlling said present at the detector.

6. An air speed indicator comprising a Pitot head, a static head, pressure-sensitive indicating means operated by pneumatic pressures at the Pitot head and static head, heating means for the Pitot head, an ice-accretion detector, said detector comprising a part in which a pneumatic pressure is produced and having an aperture which becomes blocked by the ice particles to produce a change of the pneumatic pressure in said part, a pressure movable member and means for applying the pneumatic pressure in said part to the movable member, means for applying the pneumatic pressure at the Pitot head as an opposing pressure on said movable member, a bleed passage between said part and said static head and means operated by said movable member to con trol the heating means so as to provide heating of the Pitot head only when ice is present.

7. An air speed indicator having pressure-sensitive indicating means and a unitary operating device therefor, said operating device comprising a Pitot head connected to said indicating means, heating means for the Pitot head, an ice-accretion detector, and means operated by the said detector for controlling said heating means to provide heating of the Pitot head only when ice is present.

8. An air speed indicator comprising a Pitot head, pressure-sensitive indicating means operated by changes of pneumatic pressure at the Pitot head, an ice-accretion detector, a housing carrying said Pitot head and said detector, said detector comprising a part having an aperture which becomes blocked by the ice particles to produce a change of pneumatic pressure in said part and a movable member subjected to said changes of pneumatic pressure in said part, a single electric heatin means for heating both the Pitot head and the said part of the ice-accretion detector and means in said housing and operated by said movable member for controlling said heating means to apply heat only when ice is present at the detector.

WILLIAM HELMORE. 

